Transmitters in radio communication systems are designed such that the circuit size is reduced. Use of the power amplifier in a transmitter in the saturation region giving a high efficiency increases nonlinear distortions.
A LUT-type predistortion system that uses lookup tables (LUTs) may be adapted to suppress the nonlinear distortions and reduce adjacent channel leakage ratio (ACLR). In the LUT-type predistortion system, a previously distorted signal (predistortion signal) is input to the power amplifier to reduce the distortions of the output from the power amplifier. Distortion compensation coefficients corresponding to the amplitudes and/or powers of the transmitted signal are held in the LUTs and are multiplied by the transmitted signal to generate an optimum predistortion signal.
Related techniques are disclosed in Japanese Laid-open Patent Publication Nos. 2012-39235 and 2012-90158, the entirety of each of which is expressly incorporated by reference herein.